1. Field of the Invention
The present invention relates to a communication resource assignment system in which a plurality of management target devices which are connected to a network and perform communication with each other request a communication resource distribution system to distribute communication resources via the network, and the communication resource distribution system accesses and reads communication resource assignment information stored in a resource assignment state managing unit, and transmits the read communication resource assignment information to the management target devices that have made a request.
Priority is claimed on Japanese Patent Application No. 2011-094063, filed Apr. 20, 2011, the contents of which are incorporated herein by reference.
2. Description of the Related Art
All patents, patent applications, patent publications, scientific articles, and the like, which will hereinafter be cited or identified in the present application, will hereby be incorporated by reference in their entirety in order to describe more fully the state of the art to which the present invention pertains.
As a concrete example to which the present invention is applied, there are communication systems that conform to ISA100.11a and WirelessHART which are industrial wireless standards. However, the present invention is not specific only to wireless communication but can be widely applied to a general system in which a center collectively performs assignment, management, and distribution of communication resources.
A management target device that configures a communication system needs to acquire communication resources to use itself in some way. In a communication resource assignment system for which the present invention is intended, each management target device does not acquire communication resources, a resource management mechanism that collectively manages communication resources of the system is present in the system, and the resource management mechanism assigns necessary communication resources to each device.
Generally, communication resources refer to communication timing (time) or a communication path (space), and in case of a radio communication system, a radio channel (frequency) for communication is further included. Further, even when unique resources depending on each communication system are present, the unique resources are treated as communication resources in the present invention.
FIG. 9 is a functional block diagram illustrating a communication resource assignment system in accordance with the related art. The communication resource assignment system includes a plurality of management target devices 21 to 25 which are connected to a network 10 and perform communication with each other. The management target devices 21 to 25 transmit communication resource requests Q requesting communication resources to a communication resource assignment/distribution system 30. The communication resource assignment/distribution system 30 has a functional configuration of transmitting communication resource assignment information R to a management target device that has transmitted the communication resource request Q.
In the related art, the single communication resource assignment/distribution system 30 assigns and manages the communication resources and distributes the communication resources to the management target devices. Specifically, the communication resource assignment/distribution system 30 accumulates communication network information or communication quality information from each of the management target devices 21 to 25 as cumulative information. The communication resource assignment/distribution system 30 assigns communication resources determined to be optimal according to a predetermined evaluation criterion with reference to the cumulative information to a management target device which is a request source of the resource assignment request Q and an associated management target device as necessary in response to the resource assignment request Q from each of the management target devices 21 to 25.
The communication resource assignment/distribution system 30 includes a communication unit 31 that performs communication (including a communication protocol process) with the outside, a communication resource assignment algorithm 32 that decides resources to be actually assigned according to a predetermined criterion, and a resource assignment state managing unit 33 that holds an assignment state of the communication resources.
FIG. 10 is a sequence diagram describing an operation of the communication resource assignment system of FIG. 9.
In sequence s1, the management target device 21 transmits the communication resource assignment request Q to the communication resource assignment/distribution system 30. The communication unit 31 of the communication resource assignment/distribution system 30 receives the communication resource assignment request Q from the management target device 21, and transfers the information to the communication resource assignment algorithm 32.
In sequence s2, the communication resource assignment algorithm 32 checks resource assignment methods or various restrictions which are set in advance, and decides communication resources to be assigned to a device of a request source and communication resources that need to be assigned to another device (for example, a data relay device) in response to the request of the management target device.
In sequence s3, the communication resource assignment algorithm 32 designates the type and amount of necessary resources, accesses the resource assignment state managing unit 33 of a database configuration, and searches for non-assigned (non-used) resources necessary for assignment of the communication resources.
In sequence s4, the resource assignment state managing unit 33 notifies the communication resource assignment algorithm 32 of the resource information search result that can be assigned.
In sequence s5, the communication resource assignment algorithm 32 that has received the search result notice marks resource information stored in the resource assignment state managing unit 33 to represent that the resources have been assigned. Further, the communication resource assignment algorithm 32 distributes the communication resources by transmitting the communication resource assignment information R which is the search result of resource information that can be assigned to the management target device 21 of the resource request source and an associated device.
For management of communication resources on mobile devices in an environment in which a communication environment dynamically changes, for example, in a radio network, a method in which a communication resource management system automatically assigns communication resources based on a predetermined restriction or criterion which is decided in advance like the conventional method is useful as a predetermined communication quality securing means in terms of operational management.
However, when a mutual communication system is introduced to a management target device group in which an application is installed such that an installation position of a sensor or the like is fixed like a sensor network in an industrial system, and a data transmission amount or timing thereof (period) is already decided at the stage of system design, if the conventional method of dynamically assigning the communication resources to each management target device group is applied as is, the following problems occur.
(1) Automatically set resource assignment may be different from an operator's expectation.
In a system in which each communication device is arranged at a previously set position and performs communication at a previously set period, a user can be involved in assigning the communication resources such as a communication path or communication timing, and thus construction of a desired communication system is expected to be implemented.
However, in a system in which communication resources are automatically assigned according to a predetermined rule as in the conventional method, the automatically constructed communication resource assignment may be different from the operator's expectation.
Even in the conventional method, the above problem may be solved by allowing a detailed constraint condition to be input to the communication resource assignment algorithm and allowing the user to set the condition as he/she likes. In this case, however, time and effort for system setting increase.
(2) It is difficult to develop or exchange a resource assignment algorithm.
The communication resource assignment algorithm operates as a software component on a device in which a communication resource assignment/distribution system operates. In this operation environment, when algorithms performing different assignment techniques, that is, algorithms having different constraint conditions or different evaluation criteria for optimization, are introduced, it is necessary to implement and introduce an algorithm for each assignment technique. Thus, it is necessary to create software operating on the communication resource assignment/distribution system for each new algorithm.
When the communication system operates in a general-purpose operation environment such as a personal computer (PC), it is not problematic to develop software. However, when the communication system operates on a special device such as an embedded device, it is difficult to develop software, and the system has to be completely stopped when software is installed.
(3) A communication resource assignment/distribution system is required to have predetermined calculation capability, and thus a restriction occurs in the system configuration. Specifically, a process of checking an associated resource assignment state, searching for free resources satisfying a constraint condition, and performing a data operation according to a predetermined condition is generally performed.
When the number of management target devices or the amount of resources managed by the communication resource assignment/distribution system is small, it is not problematic. However, in a system in which hundreds or thousands of management target devices are managed or a system in which communication resources to be assigned are complexly associated, the communication resource assignment/distribution system needs to have a huge amount of resources in terms of hardware such as calculation capability or a memory.
It is desirable to construct an environment in which the communication resource assignment/distribution system implements a high-performance data process. However, when there is a restriction on processing performance due to a device installation environment (for example, explosion protection) or the cost, in order to secure an originally necessary calculation capability, the number of management target devices acceptable by the system or a communication band that can be assigned may be restricted due to the processing performance of the communication resource assignment/management system.
(4) Overhead is present in a resource management system.
In the conventional method, in order to assign communication resources regarded as being optimal, it is necessary to collect information associated with a communication state before assignment of communication resources. Even in a system in which a communication environment does not dynamically change or in a system in which it is known that a change is small, when a management system based on the assumption of a dynamic environment change is introduced, it is necessary to perform the maintenance of management information which was originally unnecessary, and thus overhead occurs.